1352
Anal. Chem. 1986, 58, 1352-1355
of the ions for the 12.6-min component, which corroborates their unique origin. The corresponding extracted ion current profiles and TIC for the sample obtained for the inhaler (Figure 4B) show the same ions that are characteristic of (SI-(+)-and (R)-(-)methamphetamine ( m / z 320,228 and 176). Careful inspection of the extracted ion current profiles (Figure 4B) reveals a coincidence of retention time for the small ion current observed at 12.6 min, and a correspondence of relative abundance between the ions, as was observed for the authentic sample (Figure 4A). These results confirm the identity of the minor component as arising from low-level enantiomeric contamination of the sample.
CONCLUSION This work shows that detection and positive identification of enantiomeric contamination can be readily achieved down to a t least the 1% level. Facile and reliable analysis at this level is a result of advances in two areas: (1)the development of highly efficient methods for the resolution of enantiomers on HPLC chiral stationary phases, thus avoiding the introduction of errors from use of chiral reagents, and (2) the development of effective thermospray LC/MS interfacing with capability for “filament-on” detection, which allows use of normal phase chromatographic systems. ACKNOWLEDGMENT E.D.L. and J.D.H. thank M. L. Vestal and Vectec Corp., for the generous loan of a thermospray LC/MS interface and power supply.
Registry No. (RS)-I, 4846-07-5;(S)-(t)-I, 537-46-2;@)-(-)-I, 33817-09-3; 2-naphthyl chloroformate, 7693-50-7.
LITERATURE CITED (1) @I, J. J . roxicoi. clin. roxicol. 1982, 19, 517. (2) Liu, J. H.; Ramesh, H.; Tsay, J. T.; Ku, W. W.; Fitzgerald, M. P.; Ange10% S. A.; Llns, C. L. K. J . Forensic Scl. 1981, 26,656. (3) Wells, C. E. J . Assoc. Off. Anal. Chem. 1070, 53, 113. (4) Matin, S. B.; Rowland, M.; Castagnoli, J., Jr. J . Pharm. Sci. 1973, 62, 821. (5) Pohl, L. R.; Trager, W. F. J . Med. Chem. 1973, 16, 475. (6) Nichols, D. E.; Barfknecht, C. F.; Rusterholz, D. B.; Benington, R.; Morin, R. D. J . Med. Chem. 1973, 16, ‘480. (7) Gal, J. J . Pharm. Sci. 1077, 66, 169. (8) Barksdale, J. M.; Clark, C. R. J . Chromatogr. Sci. 1985, 23, 176. (9) Weber, H.; Spahn, H.; Mutschler, E. J . Chromatogr. 1984, 307, 145. (10) Liu, K.; Ku, W. K.; Fitzgerald, M. P.J . Assoc. Off. Anal. Chem. 1983, 66, 1443. (11) Liu, K.; Ku, W. K. Anal. Chem. 1981, 53,2180. (12) Liu, K.; Ku, W. K.; Tsay, J. T.; Fitzgerald, M. P.; Kim, S.J . Forensic Scl. 1982, 27, 39. (13) Pirkle, W. H.; Finn, J. M.; Schreiner, J. L.; Hemper, 8. C. J . Am. Chem. SOC. 1981, 103,3964. (14) Walner, I. W.; Doyle, T. D. LC Mag. 1984, 2 , 88. (15) Doyle, T. D.; Adams, W. M.; Fry, F. S.,Jr.; Wainer, I. W. J . Liquid Chromatogr ., in press. (16) Covey, T. R.; Crowther, J. B.; Dewey, E. A.; Henion, J. D. Anal. Chem. 1985, 56, 474. (17) Crowther, J. B.; Covey, T. R.; Dewey, E. A.; Henlon, J. D. Anal. Chem. 1984, 56, 2921. (18) Vestal, M. L. Science 1984, 226, 275. (19) Voyksner, R. D.; Bursey, J. T.; Hines, J. W. J . Chromatogr. 1985, 323,383. (20) Liberato, D. J.; Fenselau, C. C.; Vestal, M. L.; Yergey, A. L. Anal. Chem. 1983, 55, 1741. (21) Garteiz, D. A.; Vestal, M. L. LC Mag. 1085, 3 , 334.
RECEIVED for review January 9,1986. Accepted February 21, 1986.
Carboxymethylated Polyethylenimine-Polymethylenepolyphenylene Isocyanate Chelating Ion Exchange Resin Preconcentration for Inductively Coupled Plasma Spectrometry Zs. Horviith’ and Ramon M. Barnes* Department of Chemistry, GRC Towers, University of Massachusetts, Amherst, Massachusetts 01003-0035
A carboxymethylatedpolyethyienlmlne-polymethylenepolyphenylene Isocyanate chelating ion exchange resln was prepared, characterlred, and used for metals preconcentratlon for lnductlvely coupled plasma spectrometry. The uptake of copper, cadmlum, lead, and zinc by the resln was quantitative In the presence of high concentrationsof ammonium, caklum, magneslum, potasslum, sodium, and acetate and citrate salts. These metals could be collected from artlficial seawater, Dead Sea water, and dissolved bone wlth a recovery of nearly 100%. The resln also chelates heavy metals and rare earths. Complexed metals can be eluted from the resin column wlth strong adds. The resln does not change volume with ionic form changes and can be regenerated for repeated use.
Chelating resins containing ligands with nitrogen and oxygen donor atoms on a polymer matrix are useful analytical Permanent address: L. Eotvos University, Institute of Inorganic and Analytical Chemistry, P.O. Box 123, H-1443 Budapest, Hungary.
reagents. These ligands are capable of forming a complex with a heavy metal atom incorporated into the polymeric material ( I ) . The best known of this type of resin is Chelex-100 (2), which has a polystyrene backbone and is widely used in trace analysis for preconcentration of heavy metals. However, Chelex-100 shrinks as its ionic form and pH change; for example, the resin swells 100% in changing from hydrogen to a monovalent salt form. Therefore, precautions such as wrapping columns with tape are required (2). The shrinkage is a drawback when the resin is used for collecting heavy metals from seawater (3). Dingman et al. (4) prepared polyamine-polyurea resins, and among them was a resin formed from polyethylenimine of molecular weight of 1800. A thorough study of the synthesis of these resins was reported by Hackett (5) and Hackett and Siggia (6). The resins were prepared by reacting polyethylenimine with molecular weight of 1800 (PEI-1800) with polymethylenepolyphenylene isocyanate (PAPI) to produce a cross-linked polyamine-polyurea polymer. The ratio of PEI/PAPI of 8 to 1,which was given in grams of the reactants, showed the best properties. This polymer was used to prepare
0003-2700/86/0358-1352$01.50/00 1986 Amerlcan Chemical Society
ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Table 1. ICP-AES Wavelength and Figures of Merit element Ag
A1
Bi Ca Cd
co
Cr cu DY Fe Ga Hg In La Lu Mg Mn Mo Nd Ni Pb Th Ti U V
Zn
wavelength, nm 328.07 396.1 223.0 393.3 226.5 238.9 267.7 324.7
353.1 238.2 294.3 253.7 325.6 379.5 261.5 279.5 257.6 386.4 406.1
detection limit,"* ng mL-l 4
30 34 0.2c 2
10 25 6 3 20 12 goc
63 14
0.4 0.5c 4
31 41
221.6
15
220.3
100
274.7
334.9 385.9 292.4 213.8
55c 3 18OC 12 10
RCalculatedfrom 3 times the standard deviation of the background. * Injection method, 100 pL sample introduction. Continuous nebulization. a poly(dithi0carbamate) chelating resin (6). Anchoring of other chelating groups to the polymer was not attempted. The poly(dithi0carbamate) resin was applied widely in connection with inductively coupled plasma atomic emission spectrometry (ICP-AES) for preconcentration and separation (7). The synthesis and characterization of a carboxymethylated polyethylenimine-polymethylenepolyphenylene isocyanate (CPPI) chelating ion exchange resin are described in this article. The new resin was prepared by the reaction of a polyamine-polyurea polymer with chloroacetic acid. The separation and preconcentration of metals by this resin from different matrices and the application of the resin for ICP spectrometry are evaluated.
EXPERIMENTAL SECTION The inductively coupled plasma (ICP) instrumentation and operating conditions are given elsewhere (8). The elements, wavelengths, and figures of merit considered in this investigation are summarized in Table I. Infrared spectra were recorded with a Perkin-Elmer Model 1320 spectrophotometer. Polypropylene chromatography columns (0.7 mm i.d., 350 mm long, Bolab No. BB9194, Lake Havasu City, AZ) with cotton wool in the end of the stem were used for the resin collection of the metals. Stock solutions were prepared from high-purity metals or ACS reagent-grade chemicals. Distilled, deionized water was used throughout the experiment. The artificial seawater was purified of metals to be studied with a poly(dithiocarbamate)resin column (9),and the Dead Sea water sample was purified with poly(dithiocarbamate) and CPPI columns before being spiked with metals. The Dead Sea water matrix contained the following: Ca, 15-16 g/L; Na, 36-39 g/L; K, 8 g/L; Sr, 300 mg/L; and Mn, 3-8 mg/L. Ammonium acetate (2 M) and citrate (2 M), and sodium acetate (1 M) solutions also were purified with a poly(dithi0carbamate) column. Resin Preparation. Polyethylenimine (PEI-1800, Polysciences, Warrington, PA) was reacted with polymethylenepolyphenylene isocyanate (PAPI-135,Upjohn, LaPort, TX) to produce a cross-linked polyamine-polyurea polymer (5). As a characteristic datum the isocyanate content of PAPI was used, since isocyanate is the active group on the PAPI. A molar ratio of PEI-1800-to-
1353
isocyanate content of PAPI of 140-3.6 mol was employed for the preparation of the polyamine-polyurea polymer. The polymer was dried, ground, and sieved. The 60-100 mesh fraction was used for the preparation of the CPPI resin. To 5.00 g of polyamine-polyurea polymer, a neutralized solution of 60 g of chloroacetic acid in 150 mL water was added. The mixture was reacted at pH 8 at a controlled temperature of 80-95 "C on a water bath. During the reaction the pH decreased. The pH was readjusted to pH 8 occasionally. After the pH change stopped for 3-6 h, the resin was filtered and washed sequentially with distilled water, with 1 N nitric acid, and with distilled, deionized water, The resin was air-dried, and the dried resin was pale yellow. Resin Carboxyl Determination. A dynamic potentiometric titration curve of the resin carboxyl group could not be achieved, because the reaction equilibrium was slow. Instead, a back titration was employed. An excess of 0.1 N NaOH was poured on 1,000 g of CPPI resin. The mixture was allowed to stand for 1 h; the resin was filtered and washed with distilled water, and the excess NaOH in the filtrate was titrated with 0.1 N HC1. Resin Metal Capacity Determination. A batch method was used to determine the resin metal capacity. Triplicate 50 mg resin samples were equilibrated for 10 min by stirring with lo00 pg/mL of metal solution in the presence of ammonium acetate buffer. For Ca a 600 pg/mL solution also was used, but the capacity results were the same. For metals of higher molecular weight (Hg, Pb, Th, U), 2000 pg/mL of solution was used, so that the molar ratio of metal ion to CPPI resin was approximately constant. The After filtration metals were eluted twice with 5 mL of 2 N "0,. the eluate was diluted to 50 mL. The metals were determined by ICP-AES by continuous nebulization, and, when necessary, the solutions were diluted. When the Cu and Ca capacities were measured at pH 5.3, the resin also was washed with 100 mL of 0.1 M KNOBor NaNO,. Metal Ion Collection from Matrix Solutions. To evaluate chelation in the presence of concentrated salt matrices, recoveries from acetate and citrate solutions, artificial seawater (IO), and Dead Sea water were examined by the use of a column method. Thus, 10 pg of Cu and Zn, 20 pg of Cd, and 50 pg of Pb were mixed with 30 mL of 0.1 M ammonium acetate (pH 5.8), 0.1 M ammonium citrate (pH 4.8), artificial seawater (pH 5.12 buffered with acetate and pH 4.8 buffered with citrate), or Dead Sea water diluted twice (pH 5.09). The solutions were passed through 0.1 g of ammonium- or sodium-form CPPI resin in a polyethylene column at a flow rate of 2-5 mL/min (5.2-13 mL min-l cm-2). The resin column was washed 3 times with distilled deionized water before elution. The metals were eluted with 5 mL of 2 N "OB, and the solution was diluted to volume in a 10-mL volumetric flask with distilled, deionized water. The metals were determined by ICP-AES by injecting 1 0 0 - ~ Lvolume samples. Collection by the resin of the following elements from buffered solutions was investigated with the same method: (a) pH 5-6, Ag, Co, Fe(JII),In, La, rare earths, Mn, Ni, Ti, V(V); (b) pH 2, Bi, Fe(III), In, Ti, V(V); and (c) pH 3, Bi, Fe(III), In. A bone sample was dissolved in concentrated nitric acid and evaporated almost to dryness. The residue was dissolved in 0.5 mL of concentrated "OB and 10 mL of distilled deionized water, diluted to 100 mL, spiked with 10,20, and 100 pg of Cu, Cd, and Pb, and the pH was buffered to 4.7-5.0 with sodium acetate in the presence of 0.05 M sodium citrate. The same method as described above was applied for the collection of metals.
RESULTS AND DISCUSSION A carboxymethylated polyethylenimine-polymethylenepolyphenylene isocyanate (CPPI) chelating ion exchange resin was prepared successfully by the reaction of a polyaminepolyurea polymer with chloroacetic acid. The polyaminepolyurea polymer synthesized from PEI-1800 and PAPI following the method of Hackett (5) was easily filtered and resulted in a high metal capacity when reacted with chloroacetic acid only when the molar ratio of PEL1800 to isocyanate content of the PAPI was 1-3.6 mol. The polyamine-polyurea polymer had primary and secondary amine groups that reacted with chloroacetic acid. During the reaction aminoacetic and iminodiacetic acid functional groups were formed on the
1354
ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Table 11. Metal Capacity of the CPPI Resin
capacity, element A1 Ca Cd
co cu
Fe(I1) Fe(II1) Hg Mg
Mn Ni Pb
Th U V(V) Zn
PH
mmol/g of resin
3.3 6.0 5.0 5.0 5.0 5.0 5.0 5.0 6.0 5.0 5.0 6.0 3.5 5.0 3.3 6.0 4.9
0.118 0.127 0.440 0.343 0.715 0.253 0.279 0.323 0.0061 0.203 0.504 0.471 0.071 0.064 0.164 0.330 0.842
5.0
n.4.14
Table 111. Metal Recovery (%) from Different Matricesn sample
cu
1 2 3 4 5 6 7 8
97, 95, 93, 102 100,92,98 96, 96 loo,94 98, 99 90 105 98 mean (1-8) 97.0 no. of data 16 RSD(%) 3.9
Cd
Pb
Zn
94, 98, 94, 97 98, 100,96 95,99 97, 93 97,99 96 100 96 96.8 16 2.2
89,98 103, 100 1oo,95 96, 100 95 103 92 97.3 11 4.5
96 95, 97, 95 100,99 102,99 97, 97 95 101 95 97.5 13 2.5
Means of triplicate collections at pH 4.8-5.8. Sample identification: 1,ammonium acetate (0.1 M) pH 5.8; 2, ammonium citrate (0.1 M) pH 4.8; 3, sodium acetate (0.1 M) pH 5.5; 4, artificial seawater pH 5.12 (acetate);5, artificial seawater pH 4.8 (citrate);6, Dead Sea water pH 5.09; 7, ammonium citrate (0.1 M) + Ca to metals lo4 to 1 (2.5 mM Ca) pH 4.8; 8, ammonium citrate (0.1 M) + Ca to metals IO3 to 1 (0.25 mM Ca) pH 4.8. (I
Table IV. Resin Uptake from Acetate Buffer at pH 5-6(I
polyamine-polyurea backbone. When the IR spectra of the polyamine-polyurea polymer and the resulting compound after the reaction of the polymer with chloroacetic acid were compared, the polymer spectrum was the same as described by Hackett (5). In the spectrum of the new resin, bands occurred at 1640, 1520, 1440, and 1390 cm-' resulting from the presence of carboxylic acids. The COzH group gives a band at 1440-1395 cm-'. The symmetrical stretching band of the carboxyl ion of the zwitterion structure occurs between 1610 and 1550 cm-l and its symmetrical pair between 1410 and 1390 cm-' (11). The IR spectrum revealed that carboxyl groups attached to nitrogen were on the resin. From the structure of the starting polymer, the new resin was a carboxymethylated polyethylenimine-polymethylenepolyphenylene isocyanate (CPPI) chelating resin. The IR spectrum of ethylenediaminetetraacetic acid (EDTA) was compared to the spectrum of the CPPI resin. EDTA gave absorption bands at 1680,and 14-40, and 1390 cm-' due to the zwitterionic structure in EDTA. Thus, the similarity between the CPPI resin and EDTA is evident, since both exhibit the zwitterionic structure characteristic of amino acids. The carboxyl content measured acidimetrically varied for different batches of the resin from 1.5 to 1.9 mmol/g. Similarily, the Cu capacity varied from 0.7 to 1.0 mmol/g. From the carboxyl content and the Cu capacity data, the COOHto-Cu ratio was close to 2 to 1. However, this ligand-to-metal ratio could be an average, because the ratio of aminoacetic to iminodiacetic acid groups on the resin was unknown. The chelated metal ions can be eluted from the CPPI resin with diluted strong acids, and the resin can be regenerated for repeated use. In contrast, metals can be recovered effectively from the poly(dithi0carbamate) resin, which has the same backbone as the CPPI resin, generally after the digestion of the resin. The metal capacity measurements are summarized in Table 11. From these capacity measurements the uptake of first transition series metals follows the Irving-Williams order of the metals Mn < Fe(I1) C Co C Ni < Cu > Zn corresponding to the stability order of their complexes. The order is achieved if the donor atom of the ligand is N, or 0, or N and 0. The validity of this order can be considered as another indication of aminoacetic and iminodiacetic groups on the resin. The chelated copper could not be exchanged by alkaline ions when the resin was washed with excess of KNO, or NaN0, after the uptake of copper. The capacity for calcium decreased in the same experiment. Half of the calcium could be removed from the resin with KNO, or NaN03, indicating
uptake, element Ag
Bi
Cd
co Cr(II1)
cu
DY Fe (111) Ga
In a
%
97 46 99 97 73 99 102 88 76 75
uptake, element La Lu Mn Mo
Nd Ni Pb
Ti U V(V) Zn
%
94 96 97 53 90 94 97 80 99 85 100
Mean of triplicate collections, RSD 2.0-4.5%.
that calcium forms both an ionic bond and a chelate with the resin at pH 5.3. The iminodiacetic acid resin prepared by Hering (12) bonded calcium in the same way. Luttrell et al. (13) described an iminodiacetate ion exchange resin for which ion exchange and chelation took place with alkaline-earth metals between pH 4 and pH 6. In Table I11 data for the uptake of copper, cadmium, lead, and zinc from different matrices are summarized. The pH of the solutions varied with the matrix between 4.8 and 5.8. From the results of these experiments the copper, cadmium, lead, and zinc uptake of the resin is quantitative in the presence of a high concentration of ammonium, calcium, magnesium, potassium, and sodium, and acetate and citrate salts. These metals could be collected from artificial seawater and Dead Sea water with a recovery of nearly 100%. The molar ratios of calcium to metals in the artificial seawater experiments were lo4to 1and lo5 to 1. In the Dead Sea water experiments the molar ratios of calcium and sodium to metals were lo4to 1 and lo5to 1,respectively. The Dead Sea water contained -0.4 M calcium and -1.5 M sodium. In the presence of citrate the recoveries from a bone sample spiked with Cu, Cd, and Pb, were 92,96, and 94%, respectively. The bone contained -0.01 mol of Ca/g. These data demonstrate that the CPPI resin collects trace metals even if the matrix ionic strength is high. For this reason it can be used more advantageously than Chelex-100 for trace analyses in high concentration salt samples. Because the aminoacetic acid functional group is attached to the resin polymer along with the iminodiacetic acid and its metal chelating ability is somewhat different from that of Chelex-100, cadmium, copper, lead, and zinc are chelated by the CPPI resin preferentially to other transition elements.
ANALYTICAL CHEMISTRY, VOL. 58, NO. 7, JUNE 1986
Table V. Metal Recovery (%) from Acetate and Citrate Buffers on CPPI Resin and IDAEC acetate (pH 5-6)
CPPI element Ag
A1
Bi Cd co Cr(II1)
cu
Fe(II1) Ga La
Mn Ni Pb Ti
V(V)
Zn
resin 97 65 46 99 98 73 99 88 76 94 97 94 97 80 85
100
citrate (pH 4.9)
CPPI IDAEC
resin
IDAEC
80 103 98 99 99 98 85 95 97 97 96
99 97
99 93
99
97
101
97
100
94 85 99
100
99
In Table IV uptake data for 21 different metals from a pH 5-6 solution buffered with ammonium or sodium acetate are summarized. Based on these results the resin can be applied for preconcentration of the following metal ions: Ag, Cd, Co, Cu, La, Mn, Pb, rare earths, and Zn. The uptake values from pH 2 and pH 3 solutions were 74% and 93% for Bi, 93% and 88% for Fe(III), and 79% and 80% for In, respectively, and 46% for Ti and 73% for V(V) from pH 2 solution. Therefore, the uptake is quantitative only for Fe(II1) at pH 2 and for Bi at pH 3. The application of iminodiacetic acid ethylcellulose (IDAEC) for metal preconcentration and ICP-AES was described recently (8). The metal uptake of IDAEC from acetate solution at pH 5-6 is compared in Table V with that of the CPPI resin. Based on the results of these uptake studies, the two chelating exchangers behave similarly. The high uptake of Bi, Cr(III), Ti, and Ga by IDAEC can be ascribed to the cellulose, which can form OH bridges with these easily hydrolizable ions. This behavior is an advantage of the cellulose exchanger. Thus, both the CPPI resin and the IDAEC can be applied to the collection of transition and rare-earth metal ions as well as metals with filled d orbitals like Zn, Cd, and Hg. The best pH range for both is 5-8, and the chelated metals can be eluted from both chelating materials with dilute strong acids. The recovery of cadmium, cobalt, copper, lead, and zinc from citrate solution (Table V) demonstrates that both chelating ion exchangers can be used equally well for the collection of these metals in the presence of citrate. However, because these ion exchangers have N and 0 donor atoms, they are less
1355
capable of multielement preconcentration than the poly(dithiocarbamate) resin (7). The poly(dithi0carbamate) resin forms chelates with more than 50 elements, including antimony, arsenic, selenium, and tellurium, and can be applied over a pH range of 2-12 for the collection of trace metals. Since the metals are strongly bound as S chelates and cannot be eluted readily from the resin with acids, the poly(dithi0carbamate) resin must be partially or totally digested before the determination of trace metals. The CPPI resin is a good collector of heavy metal ions from different matrices and can be used for preconcentration for ICP spectrometry or other metal analysis techniques. Since the CPPI resin has the capability to bind the same metals that can be collected with Chelex-100 without undergoing volume changes when its ionic form is altered, it can be applied more advantageously for collecting trace metals from high salt matrices such as seawater, Dead Sea water, or bone. Preconcentration factors of 20 and 40 have been achieved in the present study with the CPPI resin. Since the copper capacities of the IDAEC, poly(dithi0carbamate) resin, and CPPI resin are in the range of 0.7-1 mmol/g and the column collection flow rates can be 5-20 mL m i d cm-2 for all of them, they can be applied equally well for many trace metal analyses with preconcentration factors of >40. They can be employed for the separation of some elements in the presence of citrate as for example in the chelation of cadmium, cobalt, copper, and lead from aluminum, chromium(III), gallium, or manganese matrices. Experiments are in progress to extablish the recovery of other metals on the CPPI resin and to apply it to other trace analyses.
LITERATURE CITED Sahni, S. K.; Reedilk, J. Coord. Chem. Rev. 1884, 5 9 , 1. Bio-Rad Laboratories Product Information Bulletin 2020, 1983. Kingston, H. M.; Barnes, I . L.; Raips, T. C.; Champ, M. A. Anal. Chem. 1878, 50, 2064. Dingman, J.; Siggla, S.; Barton, C.; Hitchcock, K. Anal. Chem. 1972, 4 4 , 1351. Hackett, D. S. Diss. Abstr. Int., B 1977, 3 7 , 4430. Hackett, D. S.; Siggia, S. I n Environmental Analysis; Ewing, G. W., Ed.; Academlc Press: New York, 1977; p 253. Barnes, R. M. Biol. Trace H e m . Res. 1984, 6 , 93. HorvBth, 2s.;Barnes, R. M.;Murty, P. S. Anal. Chim. Acta 1985, 173, 305. Mahanti, H. S.; Barnes, R. M. Appi. Spectrosc. 1983, 3 7 , 401. Grasshoff, K. Methods of Seawater Analysis ; Verlag Chemie: Weinheim, and New York, 1976; p 300/b. Wilson and Wilson'sComprehensive Analytlcal Chemistry;Svehla, G., Ed.; Eisevier: Amsterdam, 1976; p 6. Hering, R ChelatbiMende lonenaustauscher;Academle-Verlag: Berlln, 1967. Luttreii, G. H.; More, C.; Kenner, T. Anal. Chem. 1871, 4 3 , 1371.
RECEIVED for review November 14,1985. Accepted February 3, 1986. Research supported by the ICP Information Newsletter.
